Our specific aim is to validate and further develop an innovative method to measure glomerular size-selectivity. We propose to use a series of novelly labeled, pre-sized inert polymers. By this method, glomerular size-selectivity measurements can be directly obtained from collected serum and urine samples. This approach will eliminate both the disadvantages associated with radioactivity and the cumbersome step of post-separating macromolecules fragments by size-exclusive chromatography. This approach will provide a glomerular size-selectivity assay kit that is safe, easy-to-use, accurate, and cost-effective while providing a diagnostic modality that is versatile for a wide range of research and clinical situations. Experiments will characterize our novel labeling system. Labeled polymer will be tested for the number of labels bond per polymer; overall change; stability to incubation in buffer with temperature variation; stability to challenge with competing chelates and in a serum environment. The optimum labeling conditions will be defined as well as the sensitivity of detection. PROPOSED COMMERCIAL APPLICATION: Research is directed toward the development of an easy-to-use and cost-effective glomerular size-selectivity assay kit, suitable for both the research and clinical marketplace. This product will provide increased assay design flexibility over current methods.